net: better IFF_XMIT_DST_RELEASE support

Testing xmit_more support with netperf and connected UDP sockets,
I found strange dst refcount false sharing.

Current handling of IFF_XMIT_DST_RELEASE is not optimal.

Dropping dst in validate_xmit_skb() is certainly too late in case
packet was queued by cpu X but dequeued by cpu Y

The logical point to take care of drop/force is in __dev_queue_xmit()
before even taking qdisc lock.

As Julian Anastasov pointed out, need for skb_dst() might come from some
packet schedulers or classifiers.

This patch adds new helper to cleanly express needs of various drivers
or qdiscs/classifiers.

Drivers that need skb_dst() in their ndo_start_xmit() should call
following helper in their setup instead of the prior :

	dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
->
	netif_keep_dst(dev);

Instead of using a single bit, we use two bits, one being
eventually rebuilt in bonding/team drivers.

The other one, is permanent and blocks IFF_XMIT_DST_RELEASE being
rebuilt in bonding/team. Eventually, we could add something
smarter later.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 3 insertions, 3 deletions

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 0485ef18d254..12055fdbe716 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -510,7 +510,7 @@ static int ipgre_tunnel_init(struct net_device *dev)
         memcpy(dev->broadcast, &iph->daddr, 4);
 
         dev->flags              = IFF_NOARP;
-        dev->priv_flags         &= ~IFF_XMIT_DST_RELEASE;
+        netif_keep_dst(dev);
         dev->addr_len           = 4;
 
         if (iph->daddr) {
diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
index e453cb724a95..3e861011e4a3 100644
--- a/net/ipv4/ip_vti.c
+++ b/net/ipv4/ip_vti.c
@@ -364,7 +364,7 @@ static int vti_tunnel_init(struct net_device *dev)
         dev->iflink             = 0;
         dev->addr_len           = 4;
         dev->features           |= NETIF_F_LLTX;
-        dev->priv_flags         &= ~IFF_XMIT_DST_RELEASE;
+        netif_keep_dst(dev);
 
         return ip_tunnel_init(dev);
 }
diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
index ea88ab3102a8..37096d64730e 100644
--- a/net/ipv4/ipip.c
+++ b/net/ipv4/ipip.c
@@ -289,7 +289,7 @@ static void ipip_tunnel_setup(struct net_device *dev)
         dev->iflink             = 0;
         dev->addr_len           = 4;
         dev->features           |= NETIF_F_LLTX;
-        dev->priv_flags         &= ~IFF_XMIT_DST_RELEASE;
+        netif_keep_dst(dev);
 
         dev->features           |= IPIP_FEATURES;
         dev->hw_features        |= IPIP_FEATURES;